β-BaB₂O₄ with special cut-angle applied to single crystal cascaded third-harmonic generation

High-efficiency single crystal cascaded third-harmonic generation (THG) was realized in β-BaB₂O₄ (BBO) material with special cut-angle. By analyzing effective nonlinear optical coefficient (d_eff) of the cascaded THG process, which was composed by type-Ⅱ frequency doubling and type-I sum-frequency, the optimum phase matching (PM) direction in BBO crystal was determined to be (θ=32.1°, φ=11°). With an optimized 9-mm long sample which was processed along this direction, the highest cascaded THG conversion efficiency reached 42.3%, which is much superior to the similar components reported previously, including ADP, KDP, and Gd_xY_1-xCOB crystals.